With rapid development of the electronic information industry, a circuit board is required to have a lower dielectric constant and a lower dielectric loss, so as to make the circuit board have faster propagation speed and smaller propagation loss. For example, printed circuit boards are usually composed of resin and glass fiber. The resin for the printed circuit boards generally have good dielectric properties and can meet the needs of the printed circuit boards. Nowadays, for electric vehicles prevalent throughout the world, electric loss and calorific value of their battery pack system as the core are the bottleneck of restricting their development. Therefore, the dielectric properties of the glass fiber become key factors that restrict performance improvement of the printed circuit boards and batteries of new energy vehicles.
At present, the glass fiber commonly applied to circuit boards in the world mainly includes E glass fiber and D glass fiber. The E glass fiber is composed of: 52%˜56% of SiO2, 12%˜16% of Al2O3, 5%˜10% of B2O3, 16%˜25% of CaO, 0˜5.0% of MgO and 3%˜5% of Na2O+K2O. The E glass fiber has good machinability, excellent water resistance, low price and other advantages. However, its dielectric constant is high, which is about 6.7, and its dielectric loss is greater, which is more than 10−3. Thus the E glass fiber cannot meet the requirements for high density and high-speed information processing.
The D glass fiber is composed of: 72%˜76% of SiO2, 0%˜5% of Al2O3, 20%˜25% of B2O3 and 3%˜5% of Na2O+K2O. Its dielectric constant is about 4.1 and the dielectric loss is about 8×10−4. But the D glass fiber has the following disadvantages: (1) comparing with the E glass fiber, the D glass fiber has higher content of SiO2, resulting in that drilling performance of D glass fiber reinforced laminate is poor, which is not conductive to the subsequent machining; (2) the D glass fiber has a high glass softening point and poor fusibility, and is easy to produce veins and bubbles, resulting in problems such as difficult fiber drawing and more broken glass fiber in the spinning process, therefore, productivity and operationality are very poor, the production cost is high, and mass production is not easy; (3) the D glass fiber has a high melting temperature and a high fiber drawing temperature, generally more than 1400° C., is very strict in kiln quality, and will reduce the service life of the kiln; and (4) the D glass fiber has poor water resistance, and is easy to cause peeling of fiber and resin.
In order to obtain a glass fiber with better comprehensive performance, development of a glass fiber for printed circuit boards whose dielectric properties are comparable to those of the D glass fiber, for example, the dielectric constant is less than 4.5 and the dielectric loss is less than 8×10−3, but whose manufacturability and operability are excellent, for example, the fiber drawing temperature is not more than 1350° C. and a difference between the fiber drawing temperature and the ceiling temperature of devitrification is greater than 50° C., and whose water resistance is comparable to that of the E glass fiber becomes one research focus.
The Chinese Patent Application No. CNO2810477.3 discloses a low dielectric constant glass fiber, typically composed of: 53% of SiO2, 15.8% of Al2O3, 19.6% of B2O3, 5.3% of CaO, 3.9% of MgO, 0.5% of Na2O+K2O and 1.2% of P2O5. The dielectric constant of this glass fiber is as high as 4.9, and P2O5 is added thereto which easily corrodes the kiln, resulting in higher requirements for the kiln.
The Chinese Patent Application No. CN96194439.0 discloses a low dielectric constant glass fiber, by weight, including: SiO2 50%˜60%, Al2O3 10%˜20%, B2O3 20%˜30%, CaO 0˜5%, MgO 0˜4%, Li2O+Na2O+K2O 0˜0.5% and TiO2 0.5%˜5%. In this glass fiber, the content of CaO is reduced, its dielectric constant is about 4.2˜4.5, and in order to improve melting performance, TiO2 is introduced into the glass fiber. But too high content of TiO2 will seriously affect the color of the glass fiber, which restricts applications thereof.
The Chinese Patent Application No. CN200780048402.7 discloses a low dielectric constant glass fiber, composed of: SiO2 52%˜60%, Al2O3 11%˜16%, B2O3 20%˜30% and CaO 4˜8%, its dielectric loss is ≦5×10−4, but as the content of CaO is higher, resulting in that the dielectric constant is still high, which is 4.5˜5.
The Chinese Patent Application No. CN200610166224.5 discloses a low dielectric constant glass fiber, composed of: 50%˜60% of SiO2, 6%˜9.5% of Al2O3, 30.5%˜35% of B2O3, 0˜5% of CaO, 0˜5% of ZnO and 0.5%˜5% of TiO2, where ZnO replaces part of the functions of CaO and MgO, to make the dielectric constant of the glass fiber reduced to 3.9˜4.4, and the dielectric loss is 4×10−4˜8.5×10−4. But the fiber drawing temperature of the glass fiber is higher, generally greater than 1350° C., and the content of B2O3 is higher, which not only pollutes environments but also easily causes great composition fluctuation and increases corrosion to the kiln. In addition, the water resistance of the glass fiber is also poor.
The Chinese Patent Application No. CN200910216020.1 discloses a low dielectric constant glass fiber, composed of: 50%˜60% of SiO2, 12%˜18% of Al2O3, 21%˜27% of B2O3, 0˜1.8% of CaO, 0.5%˜3.2% of MgO, 0.5%˜3.2% of ZnO, 0.4%˜4% of TiO2, 0.5%˜3% of CaF2 and 0.2%˜0.6% of CeO. This glass fiber has good water resistance and good adhesion to resin, is easy for subsequent machining, has the dielectric constant of 4.2˜4.6, and has other advantages. But its dielectric loss is still high, which is 10×10−4˜12×10−4, and it's content of TiO2 is high, which is not conductive to the glass color.